Setter allows to change form values according to selected values in different fields.

// Single value
condition: { when: 'x', is: 'y', then: { set: { [field]: value } } }
// Multiple values
condition: {
when: 'x',
is: 'y',
then: { set: { [field1]: value1, [field2]: value2 } }
}

Set is a object consists of field names as keys and values as values. You can change any form field value from any conditional action.